In the tech realm: I'd spend my time doing optimization work for open-source projects. It's fun, and you get to show some objective results. I'd probably do that until I had some sort of concrete idea for a cool project or some kind of project that might benefit the world somehow.

Or maybe I'd just leave tech behind entirely and do volunteer work.

But I feel like that's a one-way street. If I walked away from tech for a few years, and decided I wanted to go back... it feels like it would be very difficult.